Coating composition



Patented Feb. 14, 1939 UNITED STATES COATING ooMrosrrIoN Carl J. Borger, Norwood, Ohio, assignor, by mesne assignments, to

Interchemical Corporation,

New York, N. Y., a corporation of Ohio No Drawing. Application May 4, 1936,

Serial No. 77,807

11 Claims. (o1. 134-39) This invention relates to the art of finishing wood, metal and like surfaces with liquid finish-- ing materials such as paint, enamel, varnish, lacquer and the like; and has reference particularly to the elimination of the phenomena commonly referred to in the paint and varnish industry as silking, floating, flooding and sagging, which are frequently encountered in the formulation and application of pigmented finishes.

The scientific reasons which account for the occurrences of these difiiculties are not thoroughly understood, and phenomena therefore must be described largely in relation to the defects which are caused in the formulation of finishing com- ]5 positions, in the application of the liquids to particular surfaces to be finished, and in relation to the defects in the final appearances of the surfaces which have been finished. V

The problems of silking and floating are encountered generally in the dipping and brush methods of applying finishes, as distinguished from the conventional spraying method. As the term is used in the industry, silking refers to a defect characterized by unintentional variation 3 in color in which the final appearance of the surface is of an uneven, moire effect. The variation in the appearancemay come about through unevenness of color tone or unevenness of color intensity. The problem is a difficult one to eliminate when uniformity in the color appearance is intended or requisite.

A common occurrence identified as silking is the presence of streaks of colors of different shades. These variations usually are not sharp as or very marked, yet the lack of uniformity of color of the finished piece may be so noticeable that the surfaces either have to bedone over, or the articles must be scrapped. Obviously, the larger the surface in which the defect of silking 40 is present, the more noticeable is any general variation in color. When the variations in the color in the silk surface are of banded or streaked formation, the difliculty sometimes is referred to as fst'reaking.

The characteristic phenomenon of silking frequently is most pronounced when articles are dipped in a bath of the pigmented composition with which they are to be coated. Generally, an article to be finished by dipping is immersed in a bath of coating liquid for only a few moments, then withdrawn and allowed to drain for a period, after which it may be dried in the air or baked in a heated atmosphere. It usually is Within the ten or twentyminute period after dipping, before appreciable drying has commenced, that the characteristic silked appearance develops, if the potential defect is present.

Certain pigmented-vehicle combinations, it may be mentioned, are more apt to silk than othersfor example, in the application of the green en- 6 amel similar to the green with which metal filing cabinetsare frequently covered, the problem is particularly acute, yet it is not possible beforehand to determine the danger.

By reason of the verticality of the articles as 0 they are withdrawn from the dipping tank, and the general downward movement of flow of excess finish from. the articles, a banded or parallel relation of streaks is noticed. Microscopic examination of these streaked variations tends to disclose actual physical separation of the various pigments entering into the color combination. For example, with a green made up of blue and yellow pigments, in one zone or one streak, the blue particies may tend to predominate in color, 20 Whereas in another zone the yellow particles may appear to be most pronounced. Of course, the occurrence of the phenomenon causes the rejection of many articles and results in serious economic losses. Prolonged grinding, and other at- 25 tempts to increase the intimacy of the relation between the pigment particles and the vehicle usually have not been found to be helpful.

The terms floating or flooding relate to the appearanceof coating compositions when the 30 compositions exhibiting such phenomena are contained within a dipping tank or Vessel. An analogy perhaps best describes the appearance. When one places a drop or two of oil upon the surface of water in the sunlight, a wide variety 35 of colors is noticeable as the oil film covers the water surface. The brilliance of the variety of colors usually is greatly subdued in the case of floating but uniformity of color in the finish of the articles treated in the baths in which 40 floating takes place is extremely difiicult to obtain. .As articles being finished are Withdrawn from the baths in which floating is present, the surfaces pass through zones of the various separated colors, and evenness in color tone is relatively impossible.

In general, it may be stated that when the phenomenon of floating or flooding is noticed in the dipping tank, the defect of silking will be noticed in the finished surface. is particularly apparent when the given liquid in a dipping tank has been agitated and then the liquid allowed to remain quiescent for an appreciable period, say an hour or so. It should be understood, however, that"silking is not the 55 Floating 50 sequel -to floating. The former phenomenon is frequently noticed where the latter is absent.

Silking, floating, flooding and sagging, it may be mentioned, all are believed to be closely related as physical manifestations of the same physical or chemical phenomena. I have discovered that tri-calcium phosphate and/ or bismuth phosphate, or a mixture of these, when incorporated into pigment coating compositions, possess the peculiar capacity to eliminate the defects attendant the phenomena of floating, flooding, sagging and silking. Otherwise stated,,the present invention is based on the determination that the introduction of about 5 to '7 by weight of the total amount of pigment of tri-calcium phosphate or of bismuth phosphate, eliminates these defects in finishing compositions otherwise susceptible thereto. Bismuth phosphate, BiPO4 is relatively expensive while the tri-calcium phosphate Ca3(PO4)2 is cheap and equally as eiiicient as the former substance. For the purposes of this disclosure, therefore, the invention is expressed in terms of tri-calcium phosphate, but it is to be understood that the materials functionally are equivalent to one another, and that either, or both, may be used.

Tri-calcium phosphate and/or bismuth phosphates, so far as the paint manufacturer is concerned, are inert in respect to color, grindability, and the other incidents of formulation. Both tri-calcium phosphate and bismuth phosphate are white in color and become substantially translucent when wetted with vehicles such as oil or varnish. Neither of these agents exerts any noticeable effect upon the drying or filming characteristics of a finishing composition in which they are present.

In general, I prefer to use about 5 to 6% by weight of tri-calcium' phosphate as the antisilking or anti-floating agent. This amount is incorporated into the given finishing composition either by direct grinding therewith, in much the same manner as the pigments are ground, or it may be ground with a vehicle to produce a somewhat paste-like body and this in turn incorporated into the final liquid, as by mixing. In the latter method of preparation, typical vehicles such as rosin-wood oil, fossil gum varnishes, perilla oil varnishes, linseed oil varnishes, and synthetic resin varnishes are suitable. The paste, once prepared, need not be further milled with the composition with which it is intended to be associated, but is simply mixed therewith by stirring in the usual manner.

Generally speaking, no particular benefits are gained by the use of substantially more than 7 of tri-calcium phosphate or bismuth phosphate. Appreciably less than 5%, based on the weight of pigment, usually is not sufiicient to produce the results desired.

The difliculty of sagging frequently is encountered in dipping processes where the coating, after the clipping, and during the drying period, tends to roll or slide downwardly, and produce wave-like accumulations. The appearance of a sagged coating is analogous to the appearance of water running down a substantially vertical surface, though to a less marked degree. About 5% of tricalcium phosphate assists greatly in over coming this difficulty and causes the coating to assume an even and uniform distribution over the surface of the dipped article.

It is thought from the theoretical point of view that the tri-calcium phosphate and the bismuth phosphate operate to produce the desired results by increasing the wetability of the pigment components entering into the composition. A reduction in the value of the interfacial tension between the pigment particles and the liquid component of the particular finish being formulated enables the pigmented particles to become thoroughly wetted and thereby sustained in stable dispersion throughout the volume of liquid. In practice, the difliculty resides in the fact that it is impossible to determine beforehand what pigments, or coating compositions, will be susceptible to the phenomena referred to. In these instances, the paste admixtures comprised of tricalcium phosphate and/or bismuth phosphate, or both, in suitable vehicles, enable the defects to be corrected in a simple manner after they have been found to exist.

Having described my invention, I claim:

1. A new composition of matter for use in pigmented coating compositions to prevent the phenomena of silking, sagging, flooding and floating thereof, which composition comprises a vehicle which is compatible with a given coating composition and which contains tri-calcium phosphate.

2. In the art of manufacturing industrial and decorative coating compositions, the method which comprises incorporating a substance selected from the group consisting of tri-calcium and bismuth phosphate into the composition being formulated in an amount suflicient to prevent silking, floating and sagging in the coating composition after it is applied to a given surface.

3. A pigmented coating composition in which tri-calcium sufiicient to position.

4. As a new composition of matter, an inorganic phosphate selected from the group consisting of tri-calcium and bismuth phosphate ground in a vehicle selected from the group consisting of rosin wood oil, fossil gum varnish, perilla oil varnish, linseed oil varnish and synthetic resin varnishes.

5. A paste adapted to use for the prevention of. silking, floating and sagging of pigmented coating compositions, which paste comprises tricalcium phosphate ground in a vehicle of a type compatible with a given pigmented coating composition.

prevent silking of the coating com- 6. The method of eliminating the phenomena of silking, floating and sagging a pigmented coating composition, which method comprises, incorporating tri-calcium phosphate into said pigmented coating composition, in an amount suflicient to prevent said phenomenon.

'7. The method of preparing an enamel, paint, varnish or like coating composition which will not exhibit the tendency to silk, float or sag during drying, which method comprises, grinding said coating composition with a substance containing tri-calcium phosphate in an amount suificient to prevent the tendency of the coating composition to silk, float or sag.

8. A pigmented coating composition containing about 5% of the weight of the total pigments in said composition of an inorganic phosphate selected from the group consisting of tri-calcium phosphate and bismuth phosphate.

9. A pigmented coating composition containing from about 5% to about 1 /9,% by Weight of the total pigments in said composition, of an inorganic phosphate selected from the group which consistsiof tri-calcium phosphate and bismuth phosphate.-

phosphate is present in an amount 10. An improved coating composition comprising a coating composition which contains a pigment and a vehicle and which inherently exhibits the phenomena of floating, sagging, silking or flooding, and a material selected from the group consisting of tri-calcium phosphate and bismuth phosphate which is suificient in amount to overcome the phenomena of, silking, floating, sagging or flooding, which the composition other- 10 wise exhibits.

11. A method which comprises incorporating a small quantity of material selected from the group consisting of tri-calcium phosphate and bismuth phosphate in a coating composition which has the tendency to exhibit the phenomena of silking, floating, sagging or flooding for the purpose of preventing the occurrence of the phenomenaof silking, floating, sagging or flooding in the coating composition.

CARL J. BORGER. 

